1. Field of the Invention
The present invention relates to a method of forming a group III/V semiconductor layer, and in particular to a method of forming a nitride semiconductor layer and separating the same from a substrate.
2. Description of Related Art
In the recent years, light emitting diodes (LED) and laser diodes (LD) are now prevailing in commercial use. For example, a mixture of blue and yellow phosphors made of gallium nitride (GaN) is capable of generating white light, which leads to a high luminance and substantially low power consumption over a conventional light bulb. In addition, the LED has a lifetime of more than tens of thousand hours, longer than that of the conventional light bulb.
In the process of manufacturing a GaN semiconductor LED, due to mismatched lattice constants and differential coefficients of thermal expansion between a GaN semiconductor layer and a hetero-substrate, the GaN semiconductor easily encounters the problems caused by threading dislocation and thermal stress during an epitaxy process, which drastically deteriorates luminance efficiency of the LED.
According to the prior art, a method of separating the GaN semiconductor layer from the hetero-substrate includes applying an irradiating method whereby laser beams pass through a substrate and illuminate an interlayer between the substrate and the GaN semiconductor layer. Thus, the GaN semiconductor layer and the hetero-substrate are separated. Moreover, a wet etching method can also be performed to directly remove a barrier structure between the substrate and the GaN semiconductor layer so as to weaken a connection structure therebetween and to further separate the GaN semiconductor layer from the hetero-substrate. In addition, a vapor phase etching process can be performed at a high temperature to directly remove the interlayer between the GaN semiconductor layer and the hetero-substrate. Thus, the GaN semiconductor layer and the hetero-substrate are separated.
Nevertheless, said methods are not capable of mitigating the loss in luminance efficiency of the GaN semiconductor layer due to the defects of threading dislocation and thermal stress in the epitaxy process.